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# OCR Physics B G495 Field and Particle Pictures June 21st 2011 Exam Thread watch

1. (Original post by Harry-AA)
when it's perpendicular there is no flux running through it so the change in flux is just the flux at the start.
right at the beginning of the rotation the flux being cut is close to zero

i think the emf generated on a graph would be 1/4 of a sine wave
2. (Original post by R0BMAN)
But it was a percentage of people, so you times'd 3 by 2x10^-5 to get percentage chance, then multiplied it by no. of people to get the likely number of people this will mean get cancer, then time it by 25 :/ I think. ? Might be wrong but I did consider using 0.03...
it was just number of people, not percentage
3. (Original post by kttt101)
right at the beginning of the rotation the flux being cut is close to zero
Meh, Idk, I just did the rate of change of the flux. I don't know how you could do it any other way.
4. What did people get for the section C question about the energy between the kryptonite (?) waves or something. I used E=hc/lambda but it was worth 3 marks so not sure if that was enough!
5. I refuse to go back a page because I'll see something I dont like, but for the ring cutting one, was it not just the answer from before in webers divided by 0.4?
It goes from a maximum to nothing in this quater turn so I assumed you just use faraday's equation. For my assumption I said that the rotation of the ring is unlikely to be continuous so the rate of flux cutting in the turn won't be constant, therefore it's an average. Probably wrong, I'm crap at the wordy questions.

Just to add to the answers circulating about, I got about 2600kg for the mass of uranium and I got 435 people to get cancer.

Also, 3 marks for a E=hc/lambda question? They having a laugh? I must have done this wrong surely in section C was it?
6. (Original post by rggregrgr)
What did people get for the section C question about the energy between the kryptonite (?) waves or something. I used E=hc/lambda but it was worth 3 marks so not sure if that was enough!
Glad you just put this. I did the same.
7. (Original post by kttt101)
right at the beginning of the rotation the flux being cut is close to zero

i think the emf generated on a graph would be 1/4 of a sine wave
Yes, that's what I did
8. (Original post by rggregrgr)
What did people get for the section C question about the energy between the kryptonite (?) waves or something. I used E=hc/lambda but it was worth 3 marks so not sure if that was enough!
It was an easy three marks
9. Yeah I think it was section C! About the element used for defining the metre blah blah.

On the whole I think it was an alright paper - bits of it were easy but some parts weird! And I think I've messed up the 4 mark question about the oil drop... :P
10. (Original post by Summerdays)
Yes, that's what I did
what did you actually get? I can't remember now...
11. (Original post by rggregrgr)
Yeah I think it was section C! About the element used for defining the metre blah blah.

On the whole I think it was an alright paper - bits of it were easy but some parts weird! And I think I've messed up the 4 mark question about the oil drop... :P
Erm... you mean ball?
12. (Original post by rggregrgr)
Yeah I think it was section C! About the element used for defining the metre blah blah.

On the whole I think it was an alright paper - bits of it were easy but some parts weird! And I think I've messed up the 4 mark question about the oil drop... :P
Don't remember this one. Was that the one with the Beta emitter fireing electrons at the thing on the spring?
13. (Original post by Harry-AA)
what did you actually get? I can't remember now...
I can't remember my numerical value but it was just E = hc/lambda
They didn't expect people to remember AS stuff haha.
14. for the ball on a spring... with the beta source did people put that the charge increases (ie the electrons from the beta source knock more electrons off) or that it decreases/charge is neutralised (electrons are attracted to and 'caught' by the ball
15. (Original post by Summerdays)
Erm... you mean ball?
Yes yes... sorry I just kept thinking of it as similar to Milikan's experiment. No doubt probably why it went a bit wrong!
16. (Original post by Summerdays)
I can't remember my numerical value but it was just E = hc/lambda
They didn't expect people to remember AS stuff haha.
No I mean for the induced emf question...
17. I said that the beta particle ionises the air and ions transfer charge to the ball. If the overall charge is positive, the ball moves downwards, if negative the ball moves upwards due to the electric force. An equalibrium is made where Vq/d = kx. The position is either above the initial position (if the ball is negative) or below (if positive.)
18. (Original post by kttt101)
for the ball on a spring... with the beta source did people put that the charge increases (ie the electrons from the beta source knock more electrons off) or that it decreases/charge is neutralised (electrons are attracted to and 'caught' by the ball
The second. It had already lost 8 x 10 to power of 6,7 or 8? (can't remember)
so it's only ever going to neutralise it I think.
19. (Original post by Harry-AA)
No I mean for the induced emf question...
Haha, I got soemthing like 0.00 something. I did My previous answer/0.4
20. (Original post by Summerdays)
I said that the beta particle ionises the air and ions transfer charge to the ball. If the overall charge is positive, the ball moves downwards, if negative the ball moves upwards due to the electric force. An equalibrium is made where Vq/d = kx. The position is either above the initial position (if the ball is negative) or below (if positive.)
The ball was possitive. The bottom plate that it was attracted to was the most negative of the two plates.

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